This study investigated the language development, the cognitive behaviors (such as imitation, manipulation of objects and play) and the communicative behavior of four infants from 9 to 25 months. Children were observed longitudinally on three different situations; free play with an adult, manipulation play and two-word-sentence comprehension test. The analysis of behaviors revealed that: (a) Bubbling stage is characterized as the sensory-motor action and the passive communication, (b) By the time of the first one-word utterances, children manipulate familiar objects adequately according to their conventionel use. They also communicate actively by pointing, imitation and other nonverbal behaviors, (c) Symbolic doll play precedes the emergence of the syntax. Symbolic play emerges about the time of first two-word sentences and increases with the development of the early syntax. At this stage several types of verbal communication are capable. Comprehension of two-word sentences is prior to their production.